People carry an increasing number of mobile and wearable devices. Most of these devices are able to communicate wirelessly using WI-FI®, Bluetooth®, NFC (Near-Field Communications), infrared, etc. protocols, (WI-FI is a registered certification mark of Wi-Fi Alliance, BLUETOOTH is a registered certification mark of Bluetooth SIG, Inc.) These wearable devices talk to each other and they talk to external devices outside of the body area network (BAN).
A set of wearable devices (SWD) communicating wirelessly and over a BAN will inevitably leak information about the person carrying this set. Even if the communications are encrypted and their timing, size and content (e.g., MAC (Media Access Control) addresses or other IDs) are randomized, an external observer may still be able to determine the number of communicating devices and their types.
One approach would be to detect the parts of electromagnetic and acoustic spectra used for communication and map them to typical existing consumer devices. As an example, detecting a pair of communicating Bluetooth interfaces, a single Wi-Fi interface and a single 3G device will give a weak fingerprint. If, for example, communications also include infrared this will be a much stronger (rarer) fingerprint. Such primitive fingerprinting is possible even before deep inspection of the transmissions' timing and data, and may give rise to significant privacy and anonymity concerns.